Compressor



May 10, 1960 M. L. BALcoM ET AL 2,936,108

COMPRESSOR Filed April 29, 1957 3 Sheets-Sheet 1 v Q cwf zwi/IA May 10,1960 Filed April 29, 1957 M. L. BALCOM ET AL COMPRESSOR 3 Sheets-Sheet 2INVENTORS. M/V/V//V l. @lfd/ff BY faef .aw/Affe May 10, 1960 M. L.BALcoM ET AL 2,936,108

COMPRESSOR Filed April 29, 1957 3 Sheets-Sheet 3 2,936,108 COMPRESSORManning Longley Balcom, Melrose, and George Gilbert Swain, Jr.,Marblehead, Mass., assignors to General This invention relates to a gasturbine (turboshaft) engine which is provided with an axial iiowcompressor, and in particular, to a means for simultaneously varying theposition of several rows of stator vanes in the compressor of a turbojetengine.

More power can be obtained from a gas turbine engine by providing ahigher pressure ratio compressor for the engine. However, whenever aconventional high pressure ratio compressor with iixed stator vanes isused, stall characteristics occur during various part speed conditions.This is due to the fact that when a compressor is designed for a highspeed, high pressure operating condition, the stator vanes are designedto have a particular angle of attack to give the most efficientoperation at that particular loperating condition. During starting or atsome part speed condition, the angle of attack of the front rows ofvances will become mismatched from the rows of vanes in the rear of thecompressor if the stator vanes are fixed, and, thereby create stall. Inother Words, at the part speed or 'starting condition, the rear stagescannot take the quantity of air that is being passed to it by the frontstages. Accordingly, back pressure is built up so as to choke thecompressor. In order to prevent this stall characteristic fromoccurring, adjustable stator vanes can be provided so that at thestarting or part speed condition the front stages can be closed downwith respect to the rear stages and thereby provide the correct airfoilorientation angle for the particular velocity of flowing air. By thismeans, the operating characteristics of the lcompressor are improvedunder certain operating conditions since the direction and quantity ofair flow is changed to correspond to the angle of attack of the statorvanes. This change in air flow has a direct bearing on the stallcharacteristics of an axial ow compressor. A compressor having variablestator vanes overcomes the tendency of poor performance at the oi designoperating conditions by merely adjusting the angle of attack of thestator vanes of the front rows so as to match the characteristics withthe back end rows. The position or angle of attack of 'the lstator vanesfor the various operating conditions can be scheduled as a function ofengine speed and pressure.

By making an engine construction heavy enough from States Patent,

a structural standpoint, the approach to the stall region of acompressor will not significantly effect its operation. For example, theapproach to the stall region of a compressor excites or creates pressuresurges which result in large vibrations in the structural components ofthe compressor. If the structural members are suiciently heavy, they canwithstand these large vibrations. However, a gas turbine engine having agood power to weight ratio results in an air frame having the capabilityof either carrying more gas or more pay load. A heavy structurally builtjet engine can not obtain this good power to weight ratio. However, inorder to provide the best power to weight ratio of a jet engine it isvery important that the engine be made as light as possible. The problemof approaching a stall region then takes on added signilicance.

` In `small aircraft gas turbines the-power to weight'ratio d if@ 2 isparticularly significant. For example, small gains in weight savingresult in greater weight savingpercentage for a small -engi-ne ascompared to the same saving fo large engines.

In small engines particularly, the space requirement is at a premium.For example, the rows of stator vanes of an axial flow compressor forsmall aircraft gas turbines are positioned so close together that it isdiilicult to locate the linkage for adjusting the stator vanes. I-t isan object of this invent-ion to provide a lightweight mechanical linkagearrangement for adjusting the rows of stator vanes of an axial iiowcompressor for a small aircraft gas turbine, which is 4capable ofoperating in a .minimum `amount lof space without any loss of Vaccuracyorsignilicant play between the parts.

Not only is 'the degree of accuracy a requirement in positioning andcontrolling the angular setting of the rows #of variable :stator vanesin relatively small compressors, but provision .must be made to minimizebacklash and error which result from the eiect of necessarymanufacturing tol'erances `and differential thermal growth between thecomponents. In other words, in a small compressor of the typecontemplated the lever arm lengths and the bellcranks are so small thatsmall movement or play will result ina relatively great angular movementof the vanes. Therefore, any errorv in machining or stack-up ofmanufacturing tolerances as well as differential thermal growth Vtheparts and to provide `the necessary accuracy and control vor the angularsetting of the rows of stator vanes of an axial flow compressor.

In a casing of a small aircraft gas turbine, and in particular thecompressor for the turbine, the circumference of the casing is so'smallthat the openings required for each of the vanes ina row of stator vanesare so rclose together that the mechanism for adjusting the vanes can ynot be connected to the vanes at the casing. For example, Athe lever armnormally fastened to the base 'of a stator vanewould interfere with `thelever arm of an adjacent stage.L It is, therefore, a further object ofthis invention to provide means for securing the lever arms of a linkagearrangement for varying the stator vanes to the base of the stator vaneat a location remote from the compressor casing. g

In a small 4aircraft gas turbine engine, radial thermal expansion `ofthe compressor casing would normally be transferred tothe actuatingmechanism for adjusting the rows `of stator vanes. of the compressor andthereby incorporate an error into the actuating mechanism. Such an errorwould not provide Afor the best angle of attack for the stator vanes.Prior art adjusting mechanisms have not been successful in minimizing oreliminating this error. It is, therefore, still a further object of thisinvention to provide a support ring -for supporting an actuating ring,which support ring is not subject to the radial thermal expansions ofthe compressor.

' It is a more specic object of this invention to lprovide a 'supportring for supporting the actuating ring and stator vanes,'which supportring is positioned and lconstructed in such a manner as to permit radialthermal expansion of the compressor casing and radial movement of theshafts of the vanes with respect to the support -r-ing withouttransmitting such movement to the support ring, and to provide a stablesupportV for the actuating ring.

Briey stated, in laccordance with one aspect ofour invention, Vweprovide stator vanes with elongated shafts tioned close together. vtheshafts 24 at the compressor casing would interfere for-relative thermalexpansion with an actuating ring. An

actuating ring for each stage is circumferentially spaced about thecasing outwardly of the shafts of a preceding :stage of vanes, so that aminimum'axial length is required for the adjusting mechanism. In orderto locate and support the actuating rings, and to prevent transmissionto them of thermal expansion of the casing and vane shafts, we mount asupport ring in circumferentially spaced relation about each stage ofvanes. The support ring receives the spacers and shafts of that stage 1na circumferentially spaced row of openings formed therein, in radiallyslid-able relation. Each actuating ring 1s rotatably mounted in acircumferential groove in the support ring associated with the precedingstage, upon bearing means carried thereby; however, an actuating ringfor an initial stage of vanes is preferably carried by the support ringassociated with the same stage. By these means, the actuating rings andsupport rings are not subjected to thermal expansion of the engineelements, but the actuating rings are given adequate support to sustainvane adjustment forces. i

Further objects and advantages of our invention w1ll become apparent inthe light of the -accompanying specification and drawing wherein similarparts are referred to by the same number and wherein:

Figure l is a cross sectional view of the compressor for an aircraft gasturbine showing the stator vanes and part of the mechanical linkagearrangement for adjusting the stator vanes.

Figure 2 is a plan view showing the external mechanical linkagearrangement yfor adjusting the actuating rings which extendcircumferentially about the compressor casing.

Figure 3 is a view taken on lines 3 3 of Figure 2.

Figure 4 -is a side View taken on lines 4--4 ofvFigure 2.

Figure 5 is a cross sectional view takenl on llnes 5 5 of Figure 2.

Figure 6 is a view taken on lines 6-6 of Figure 1.

Figure 7 is a view taken on lines 7--7 of Figure 1.

Figure 8 is a fragmentary view of a lever arm and shaft.

Referring to the figures, and in particular to Figures 1 and 2, thenumeral 10 generally refers to an axial owv compressor for an aircraftgas turbine. The compressor is provided w-ith an inlet 11 and acompressor casing 12. A row of stator vanes is shown vat 14 of whichthere can be any number. Of this number, all or a portion of the rowsmay be made adjustable. Adjacent to one row of stator vanes is a row ofrotor blades of which there can be any number of rows. The casing 12 isprovided with a plurality of circular openings 16. Each of the circularopenings are provided with a seat 18. The base of each blade 14 lisprovided with a bearing surface 20 adapted to be journaled on one of theseats 18. Positioued between the |bearing surface and the seat 18 isbearing sheet material commonly referred to as polytetrauoroethylene.The purpose of the bearing material is to provide substantiallyfrictionless movement between the seat 1S and the bearing surface 20.Also,

fthe bearing sheet material requires no lubricant and acts as an airseal to prevent leakage of high pressure air from within the compressor.Extending radially outwardly from the base of each of the adjustablestator vanes 14 is a shaft 24 which fits loosely in the opening 16 asshown by the space 25.

Due to the fact that a compressor casing of a small aircraft gas turbineis of such small circumference, and that a large number of blades in arow are required for high pressure operation, the openings 16 must beposi- Lever arms or the like secured to with adjacent lever arms.Therefore, the shafts 24 extend radially outwardly from the casing for asubstantial distance to permit the mechanical linkage such as lever armsto be fastened thereto. However, the shafts 24 must be supported againstpivoting away from a radial position under the inuence of the moment offorce produced by the impact of fluid on vanes 14. For this purpose asupport ring 37 is provided with a plurality of openings 27 equal innumber to the openings 16. In view of the stack-up of machiningtolerances, the openings 2-7 will be misaligned from the openings 16.Therefore, the openings 16 are made oversize to loosely receive shafts24.

In View of the fact that the openings 16 are made oversize, the problemarises as to how the bending loads may be transmitted from the shafts24. This is accomplished by providing a built-up portion 28 around theopenings Ythermal expansion of the 16 upon which is milled a recess orat surface 30 so as to form a seat. Extending through each of theopenings 27 in the support ring 37 is a spacer or sleeve 32. The spacer32 is flared outwardly to form a shoulder 34 adapted to seat on thesurface 30. Any bending loads of the shaft 24 is taken in the spacer 32and transmitted to the support ring 37. The spacer 32 provides a meansfor positively locating the actuating mechanism radially and `theactuating ring in an axial directirfrri.s

In order to isolate the support rings 37 from the compressor casing 12and stator vanes 14 so as not to be subject to radial thermal expansionsthereof, the support ring is slidably mounted on spacers or sleeves 32,with the spacers abutting recesses-30 formed on the compressor casing.This construction permits the spacers to move with the thermal expansionof the compressor casing,

and the sliding lit permits the spacers 32 to move radially within thesupport ring without affecting the support rlng. This arrangementisolates the support ring 37 from the compressor casing and provides astable support for the actuator ring. This construction also Apreventsthe compressor casing and stator vanes from creating an error in theactuating mechanism. In addition, since there are several vanes in eachrow, those of shafts 24 which are horizontally inclined maintain thesupport ring 37 in a vertical direction, and those of shafts 24 whichare vertically inclined maintain the support ring in a horizontaldirection. The support ring 37 can be dimensioned with respect to theshafts so as to be positioned at a particular radial location withrespect to the compressor casing 12 without being directly connected toit, and can be regarded as being oating. Each of the support rings isprovided with an annular groove 26. However, this is true for each ofthe rows of adjustable vanes ywith the exception of the first row whichmust provide for its own actuator support ring. In that case a secondannular groove 3S is shown on the opposite side from the annular groove26.

Extending through the actuator support ring 37' transversely of theannular grooves 26 and 38 are a plurality of fixed shafts 40. Thesefixed shafts have anti friction roller bearings 42 mounted thereon inorder to support one of a plurality of actuating rings 44. The actuatingrings 44 are shown as being substantially Z-shaped with one end mountedon the anti friction bearings 42 so as to be capable of `rotationalmovement with substantially no friction. A ring 46 is shown welded, orthe like, to the vertical portion 47 of each actuating ring 44 toprovide a wide base to enable the actuating ring to take the loads,maintain its stabliity and axial alignment.

Referring also to Figure 6, the actuating ring 44 contains a tapered camslot 48, the purpose of which will be more fully hereinafter explained.A follower pin is shown at 50 for movement within each tapered slot 48.A lever arm 52 is provided for drivingly connecting each shaft 24 withan actuating ring 44. The follower pin 50 is secured in an opening 54 ofthe lever arm 52 by welding or the like. In order to maintain a closesliding tit between the marginal edges of the cam slot 48 and taper isnecmsary since the actuating ring 44 moves about an arc of Aa rcircleand the follower '50 in a plane tangent to the arc of the circle. Thiscondition will result in the follower .pin 50 becoming more out ofalignment with respect to the cam slot thereby requiring ya graduallyenlarged slot as the angle of travel increases from its neutral or zeroposition. Therefore, the taper provides for a gradually increasinglarger slot with increase in angle of travel. l

As best seen in Figures 7 and 8, each shaft 24 is -formed at itsprotruding end with two flat tapered sides S6, and with a threaded stud'60 Aextending from the shaft. An opening 55 is formed in an end of eachlever arm 52 to conform with sides S6, and is fitted over shaft 24 withan interference lit, thereby reducing the possibility of lost motionbetween these elements. A washer 58 is shownextending over each shaft 24and engaging the lever arm 52. A nut 62 is threaded on the threaded stud60 so as to engage the -washer 58. Anabutment surface 59 of spacer 32locates the radial position of the lever arm 52 with respect to thecompressor casing 12.

Referring again to Figures i and 2r, the lever arms S12 are secured tothe shafts 240i the vanes 14 in a sprung condition Vso as to bearagainst the actuating ring 44. This enables the casing along with thevanes 'to expand radially without losing the snug iit and without-thefol-` lower 50 being separated from the cam slot 48.

In order to actuate the actuator ring44 in an arc-of a circle about thecompressor casing, a clevis`64 is shown lixed to the actuating ring 44by a rivet or the-like 66. Actuator means are connected to thisclevisfor actuating the actuating ring. This actuatorv means includes .a pinand nut arrangement 68 extending through the clevis '64. Mounted on thepin and nut arrangement 68 .1s a self aligning uniball bearing 70. Ingeneral, the uniball bearing consists of a ball 69 and socket '71 withan open-` ing extending through the ball 69 to receive pm and nut '68. l

The uniball bearing 70 vis secured n one end of a turnbuckle v72 at theeye 73 to `permit the turnbuc'kle and the pin 68 to move in dierentplanes without bind-f ing, as best seen in Figures 2 and3. The -eye 73is p rovided with a stud 74 which is fitted into the main portion of theturnbuckle 72 toprovide a means forze'roln-g-ln and adusting theangle-of attack of the row of stator vanes. This turnbuckle takes careof the build-up` of manufacturing tolerances and thereby eliminates themanufacturing inaccuracy on the angle of attack of the stator vanes as aresult thereof. Another eye 75 is 1ntegrally secured to a stud 7'6 onthe other end of the turnbuckle 72. Another pin and nut arrangementalong with a self aligning uniball bearing is shown at 77 wlth theuniball being mounted in the eye 75. This Varrangement is similar inconstruction to the self aligning uniball bearing 70 and the nutarrangement 68 as shown 1n Figure 1.

Fixed to the compressor casing 12 (Figures 2, 3, 4, and is alongitudinally extending actuatorr support member 78 having brackets 79secured to the front end of the casing such 'as by bolt and nutarrangements as shown at 80. Mounted on the Vactuator support member 78are a plurality of bellcranks generally designated 81. These bellcranks81 are pivotally mounted by pins as shown at 82. Referring to Figure 5,bellcranks 81 are constructed of two similar portions, referred to asthe outer bellcrank member 83 and an inner bellcrank member 84 with theVinner and outer members being spot welded or bolted together in any wellknown manner.

The inner and outer bellcrank members 83 and 84 being secured togetheract as a unitary bellcrank. This construction permits the use ofrelatively thin lightweight material while still retaining the necessarystruc6 tural strength 'to carry the lforces transmitted to'adiust theVvanes without harmful buckling. Each bellcrank 81 terminates With outerbellcrank member 183 spaced 'from the inner bellcrank member 84 foradditional vstrength and to receive the eye 75 therebetween as shown inFigure 3. A uniball bearing is mounted in the eye 75 and is pivotallyscured to the bellcrank by the pin shown at`77 yextending through theball of the uniball.

The bellcranks 81 Aare stepped down or oifse't as shown at 85 to providesufficient clearance for the other link-` age such as the turnbuckle 72and bellcrank pivot points 82. The offset 85 permits one bellcrank tooverlie an adjacent bellcrank.

The other leg 86 of the bellcranks-Sl terminates with the outer member83 and the inner member 84 in abutting relationship rather than beingspaced. Each of the legs 86 of the bellcranks 81 are pivotallyinterconnected by'an interconnecting link 87 so 'that all of thebellcranks are adjusted in unison. The interconnecting link 87 (Figures2 and 3) is constructed of an outer portion 88 to fit over the outerbeller-ank member 83 and an inner portion 89 adapted to fit under theinner bellcrank member 84. The legs 86 of the bellcranks are pivotallysecured to the interconnecting link 87 by pins or rivets 90. Thekdistance from the pin 90 to the pivot 82 on each of the bellcranks isthe same so that during movement of the interconnecting link 87 each ofthe bellcranks travel Vthrough the same angle. However, the distance oneach of the bellcranks 81 from the pivot 82 to the pin at 77 can be thesame, or, can vary from one row of'vanes to another Adepending on thespace requirements, the

length of the lever arms 52, and the angle throughwhich the row lofvanes should travel. For example, the space at one row may not besufficient to permit las long a distance as may be desired. Also, spacerequirements may require that the lever arms be shorter. Therefore, inorder to provide the correct angle of travel for the vanes, the distancebetween the pivot 82 4and the pin 77 can be increased or decreased asdesired. Further, the operating conditions of the compressor may be suchas to require a much larger angle of travel for one row of vanes thananother row of vanes. To provide for the larger angle of travel, thelever arms 52 and the distance on the bellcrank between points 82 and'77 can be increased.

In order to provide for simultaneous actuation of bellcranks 81, onesuch bellcrank is formed with 'an extended leg portion 92, best shown inFigures 2 and 4, and forms a master bellcrank generally designated y91.The inner -and outer legs 94 and 96 of the extended leg portion 92 `arespaced from each other so as to accommodate a uniball bearing 97 similarto that shown in Figure 5.

An actuating link 98 is shown formed by inner and outer members 102 and100, one positioned on each side of the uniball bearing 97 and arms 94and 96. A-pin 104 extends through the ball portion of the uniball 97 andthe legs 94 and 96 of the master bellcrank 91, in addition to the innerlink member 102 and the outer link member 104. 'This pin can be in theform of a rivet or bolt and nut arrangement. The actuating link 98 issecured to an adjustable piston rod 106, as best seen in Figure 2. Thisconnection is made by providing the piston rod 106 with an eye 107 atthe one end so as to receive a uniball bearing therein. A pin 108extends through the inner link member 102 and the outer link member '100,in addition to the uniball bearing so as lto secure the parts together.The pin can be either in the form of a rivet or a nut andl boltarrangement.'

In order to actuate the piston rod 106, the piston rod is vmounted in anactuating cylinder 110. By proper control mechanismI the actuatingcylinder can be made kto operate the piston rod in response to theparameters of compressor and power turbine speed, inlet temperature,compressor discharge pressure, and engine control lever position.Whenever the speed, and pressure varies, to

. indicate the approach to the stall regionV of the engine, a

signal is transmitted to the actuator cylinder to thereby actuate thepiston rod 106 for actuating the linkage arrangement. Each row or stageof vanes will be adjusted to any desirable angle over a relatively widerange. It is readily apparent from the construction proposed anddescribed above that it is applicable to small engine applicationswherein lightweight parts are utilized' with a. high degree of accuracywhich is required for axial ow compressors.

When the piston rod 106 is actuated, the master bellcrank 91 is placed-in motion. Since the interconnecting link 87 interconnects the masterbellcrank with the other bellcranks 81, pivoting of the bellcranks aboutthe pivot pins at 82 is thereby initiated. The distance from the pivotalpoint 82 of the center of the bolt and nut arrangement to the center ofthe self aligning uniball bearing at 77 can be the same or vary fromstage to stage on each of the bellcranks. This length serves twofunctions, in that, from an operating consideration it might bedesirable to vary the lengths of the distances between the points at 77and 82 to vary the rows of vanes unequally; or where spaceconsiderations require that the distance between points 82 and 77 of thebellcranks be of different lengths for the various rows of vanes whileoperating conditions require that the angle of travel of the statorvanes must be equal, the lever arms 52 can be made of a length tocooperate with the length of the bellcranks to adjust the rows ofstators through equal angles.

The uniball at the various connections permits the Various member to bepivoted in different planes while still permitting a tight connectionbetween the members. Therefore, since each ofthe bellcranks are actuatedsimultaneously their motions are transmitted to each of the actuatingrings 44through the turnbuckles 72. This mo tion is then transmitted tothe levers 52 so that the vanes 14 are pivoted to the correct angle ofattack to meet the required operating conditions.

While a particular embodiment of the invention has been illustrated anddescribed, it will be obvious to` those skilled in the art that variouschanges and modifications may be made without departing from theinvention and it is intended to cover in the appended claims all suchchanges and modications that come Within the true spirit and scope ofthe invention.

What we claim as new and desire to secure by Letters Patent of theUnited States is:

1. A compressor comprising a casing, a rotor mounted for rotation aboutan axis within said casing and forming a gas path therebetween, rows ofstator vanes extending across said gas path, rows of rotor bladesmounted on said rotor axiallyspaced from said rows of stator vanes andextending across said gas path, a plurality of support ringscircumferentially spaced about said casing, each of said stator vaneshaving a shaft extending radially and loosely through a wall of saidcasing and through one of said support rings, a plurality of spacermeans each rotatably supporting said shaft of one of said stator vanesin said casing, said spacer means received in radially slidable relationin said support rings for supporting said support rings incircumferentially spaced relation to said casing and cooperating withsaid support rings `to locate the circumferential positions of saidstator vanes about said casing, a plurality of lever arms each securedto one of said shafts, and a plurality of adjusting rings drivinglyconnected for relative thermal expansion with said lever arms forrotating said shafts and said stator vanes, said support ringssupporting said adjusting rings in circumferentially spaced relation tosaid casing for rotation about said axis, such that radial movement ofsaid stator vanes and spacer means caused by thermal expansion thereofis not transmitted to said support rings and said adjusting rings. f

2. A compressor comprising a casing, a rotor mounted for rotation aboutan axis within said casing and forming a gas path therebetween, rows ofstator vanes extending across said gas path, rows of rotor bladesmounted on said rotor axially interposed between said rows of statorvanes and extending across said gas path, support ringscircumferentially spaced about said casing, each of said stator vaneshaving a shaft extending radially and loosely through a wall of saidcasing, said support rings formed with a plurality of radial openingseach receiving one of said shafts of said stator vanes, a plurality ofsleeves each disposed in one of said radial openings and receiving one iof said shafts rotatably for radial support thereof, and

a plurality of adjusting rings drivingly connected for relative thermalexpansion with said shafts for rotational adjustment of said statorvanes, said support rings supporting said adjusting rings incircumferentially spaced relation to said casing for rotation about saidaxis, said sleeves received in radially slidable relation in saidopenings for supporting said support rings in circumferentially spacedrelation to said casing, such that said sleeves transmit bending loadsfrom said vanes to said support rings, and radial movement of saidstator vanes and sleeves caused by thermal expansion thereof is nottransmitted to said support rings and said adjusting rings.

3. A compressor comprising a casing, a rotor mounted for rotation abouta longitudinal axis of said casing and forming a gas path therebetween,first and second axially Vspaced rows of stator vanes extending acrosssaid gas path, axially spaced rows of rotor blades mounted on said rotoraxially interposed between said rows of stator vanes and extendingacross said gas path, a plurality of shafts each affixed to one of saidvanes and extending radially through a wall of said casing, first andsecond support rings circumferentially spaced about said casing, saidfirst and second support rings formed with a plurality of radialopenings loosely receiving said shafts of said first and second rows ofvanes, respectively, a plurality of sleeves each received in radiallyslidable relation in one of said openings and receiving one of saidshafts, said sleeves radially supporting said shafts in said casing forrotation about axes radial to said casing, said sleeves supporting saidsupport rings for radial expansion relative thereto, at least oneactuating ring circumferentially spaced about said casing, a pluralityof lever arms drivingly connecting said actuating ring for relativethermal expansion with said shafts of said second row of vanes, saidactuating ring being supported upon said first support ring for rotationabout said axis to rotatively adjust said second row of vanes, wherebyradial thermal expansion of said casing and said vanes is nottransmitted to said support rings and said actuating ring.

References Cited in the le of this patent UNITED STATES PATENTS FranceDec. 19, 1955

